Re: [pve-devel] [RFC PATCH 2/2] common: btrfs: lower minimum amount of disks for raid10 to 2

[Daniel Kral <d.kral@proxmox.com>]

On 1/13/25 13:24, Fabio Fantoni wrote:
> btrfs profiles work differently but other hardware or software raids, 
> many users may not inform themselves well beforehand but even in the 
> case of informed users even if technically now btrfs allows lower limits 
> with the creation of raid 0 (and raid10) I think it would be better to 
> keep them at the base at the creation and then it must be the user who 
> consciously makes any subsequent conversions.

Hm, I'm still unsure about this, because AFAIK we already allow creating 
ZFS RAID0 with a single disk, which technically also isn't a "real" 
RAID0 setup itself. But fair point for RAID10, it could be irritating 
for users to have a discrepancy between the minimum disk amount of ZFS 
and BTRFS RAID10 and it'd be a bit harder to communicate that in a 
understandable manner.

> 
> regarding btrfs profiles at creation, one thing that could be useful is 
> to always put duplicate metadata (dup with single disk or raid 1 in the 
> case of raid0), if you don't want it by default maybe put it as an 
> additional option, and if you don't want that either at least add it to 
> the documentation (as a suggestion if you want greater resilience of the 
> filesystem without consuming excessive space)

Currently, the installer creates the BTRFS filesystem with the data and 
metadata both using the same profile. I also think it could be valuable 
to have an "advanced" option, which allows to set a separate profile for 
the metadata.

Feel free to send either a RFC for it (even if I can't tell you whether 
it will be accepted as it adds some complexity to the fs setup) or 
create a Bugzilla so also other users and developers can discuss it.


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